Heat sealing machine of the thermal impulse type and sealing bar therefor



June 29, 1954 N LANGER 2,682,294

' HEAT SEALING MACHINE OF THE THERMAL IMPULSE TYPE AND SEALING BARTHEREFOR V Filed Oct. 21, 1952 ....mnlllumllmi' IN V EN TOR.

Patented June 29, 1954 HEAT SEALING MACHINE 0F THERMAL IMPULSE TYPE ANDSEALING BAR THERE- FOR Nicholas Langer, New York, N.Y. ApplicationOctober 21, 1952, Serial No. 315,993

7 Claims. 1

This invention relates to the art or neat sealing thermoplasticmaterials, and, more particularly, to a novel and improved sealingdevice or bar for heat sealing machines of the thermal impulse type.

The present application is a continuation-inpart of my co-pendingapplication Serial No. 71,421, led January 18, 1949, ynow Patent No.2,630,396, granted March 3, 1953.

As disclosed in my Patent 2,460,460, heat sealing machines of thethermal impulse type essentially comprise a pair of pressure members orbars and a reciprocating mechanism therefor whereby pressure may beapplied upon two or more layers of thermoplastic lm to be heat sealedinterposed therebetween. Examples of the commercially most importantthermoplastic lms are Pliolm (rubber hydrochloride), Vinylite (acopolymer of vinyl chloride and vinyl acetate), Polythene(polyethylene), and Saran (vinyledene chloride). A heater element in theform of a thin and narrow strip of a metal of high specific resistance,such as a suitable nickel-chromium alloy known in the trade asNichrome,` is mounted on the face of at least one of said bars,constituting the operating or sealing surface of the machine. Sealingpulses of electric current may be passed through the said heater elementunder the control of a switching mechanism, the operation of which iscoordinated to that of the reciprocating mechanism of the bars.

During the operation of the machine, operation of the switchingmechanism is initiated substantially when the pressure members arriveinto their pressureeapplying position. A short pulse of current is thenpassed through the heater element, which, as a result of its lowcapacity, is heated to heat sealing temperature in a small fraction of asecond. The heat thus produced is immediately transferred by surfacecontact to the region of the thermoplastic layers compressed between thebars, causing heat sealing thereof. A short period thereafter, the heatproduced by the pulse of current is dissipated and the seal is cooledand consolidated under pressure whereby a strong and sound seal isobtained.

Heat sealing machines of the thermal impluse type provide importantadvantages over the commonly used heat sealing machines in which thesealing member is continuously maintained at a constant sealingtemperature. Due to the fact that the thermal impulse principle permitsthe sealed region to cool and toy consolidate under pressure, thequality of the seal is greatly improved. Also the thermal impulseprinciple makes it possible to readily seal films of materials, whichcannot be sealed on an industrial scale with sealing memberscontinuously maintained at constant sealing temperatures, such asparticularly Polythene and Saran.

Although heat sealing machines of the thermal impulse type providedexcellent results and achieved remarkable commercial success within ashort period after their introduction, certain practical diiculties wereexperienced when it Was desired to seal articles in which the thicknessof the layers to be sealed was subject to considerable variations. Suchwas the case, for example, when sealing gusseted bags formed from stripsof thermoplastic sheet material with a longitudinal lap seam where thenumber of layers to be sealed together in a transversely extending zonecan be 2, 3, or 4. As prior sealing bars of the thermal impulse typehave been generally rigid in character, excessive pressure was appliedto the regions where the number of layers to be sealed together was 4,While insuflicient pressure was applied to the regions where the numberof layers was only 2. While this diiculty was to some extent reduced byforming the pressure face of the second, unheated bar of an elasticmaterial it was not completely eliminated by such elastic or yieldingcharacter of the pressure bar. The same conditions prevailed whenconstructing and operating heat sealing machines of the thermal impulsetype wherein the length of the bars was accentuated, for example, inexcess of 2 feet. In machines of this type even a minor misalignment ofthe bars, departing from their exact parallelism, would be the cause ofconsiderable difference between the sealing pressures exerted by therespective ends of the bars. As sealing lengths of 42 inches, or more,are quite common today for example in producing barrel liners fromthermoplastic films, it was necessary to construct the bars and theirreciprocating mechanism with great rigidity and mechanical precision atsubstantial additional expense.

I have now discovered that the outstanding problem may be solved in aremarkably simple manner.`

It is an object of the present invention to improve heat sealingmachines of the thermal impulse type.

It is another object of the present invention to provide an improvedmachine for heat sealing thermoplastic sheet materials which isparticularly suitable for sealing articles, such as gusseted bags,wherein the thickness or the number Si of layers to be sealed in asingle operation may be subject to considerable variations.

lt is a further object of the present invention to provide a novel andimproved sealing bar suitable for heat sealing machines of the thermalimpulse type which, in contrast to the prior substantially rigid sealingbars, is characterized by a yielding and elastic sealing face, `capableoi conforming to the surface contour of the layers to be heat sealed.

Other and further objects and advantages of the present invention willbecome. apparent from the following description taken in .conjunctionwith the accompanying drawing, in which Fig. l is a side elevationalview, somewhat fragmentary in character and having `parts infsection, ofa heat sealing machine embodying the invention;

Fig. 2 is a section taken on line 2--2 of Fig. 1;

Fig. 3 is a View similar to Fig. 1 of a modified l-fembodiment of theinvention; and

Fig. 4 is a sectiontalren online A--A- of'Fig. 3. Broadly stated inaccordance with the Iprinciples of my invention, I provide a sealing barcomprising a rigid base having arelatively thick `layer of elastic,heat-resistant insulating` mal terial thereon. Upon this elastic zlayer,`there is tensioned a heater element in the form of a thin, ,1 `flexibleband of a metal of high specific resistance, the width of which ispreierably less than that ofthe elastic layer. Insome cases it isdesirable to cover the heater element and also the exposed portions oftheunderlying elasticlayer i with an additional layer of flexible,lheat-resistant v insulating material .having such surface'characteristics that the heat sealed or fused thermoplastic. materialwill not ,adhere or stick thereto.

This ,layer of 'flexible insulating Vmaterial must be sufficiently `thinto assure the` rapid transnmission of sealing `heat therethrough.

-I havefound that a sealing bar of the described type is characterizedby a sealing face `which is elastic and yielding so that it canvreadilyadapt itself to the surface contour of the'material to be sealed. It maybe employed infcomb-ination #with a pressure barhavingan elastic.pressure iface or a rigid and metallic pressure face.` In .y theflattercase, it is preferred to form a .channel in the pressure bar for thepassage of a coolant `fluid therethrough whereby. anyresiduall heat maybe rapidly and conveniently `removed from `the sealed'region of thethermoplastic layers.

'-Referring now to Figs. 1 and 2 of the drawing,

reference-numeral I generally denotes the sealing bar of theinvention-comprising a rigid base inrthe form of a metal bar I I- havinga-relatively thick layer of an `elastic and heat-resistant insulatingmaterial I2 mounted thereon. Thismaterial is of such character that itis not adversely affected by heat sealing temperatures, a suitable igrade of silicone rubber b'eihg excellently suited for thepurpose.

Upon the top face' ofelastic layer I2, there is tensioned a heaterelement I4 in the form of a narrow and exible lband of a` metal having ahigh specic resistance, such as Nichrome (a nickel base alloy containing1l-22% chromium and smaller amounts of silicon and manganese), lnconel.(a nickel base heatand oxidation-resistant alloy with approximately 13%chromium, 6% iron and small amounts of manganese, silicon and copper,and Nilvar (a ,.high-niclrel-ironalloy `with about 36% of nichel showingextremely low coeflicient of .temperature expansion) As it will beobserved in-.Fig 2,

between-bolts, I andrnetal base II;

structure is being held together, including the ends oflead. wires 20,which serve for connecting the heater element I4, into circuit with asuitable source of electrical energy. (Not shown.) A thin layer 2I offlexible, heat-resistant insulating mal':x=terial is-cemented orotherwise secured to the `top face of the sealing bar. Suitablematerials for this purpose are Teflon (polymerized tetra-.nuoro-ethylene) or Kel-F (polymerized triiiuorochloroethylene) eitherin the form of solid layers or as an impregnant for ya glassber fabric.The

provision of such layer, while notabsolutely necessary, is advantageousin that it protects-the thin and flexible heater element I4 againstVabrasion and injury and in addition, as a result of `the surfacecharacteristic of Teiionand `Kel-F,

prevents sticking of the sealing face to the `heat sealed regions.

Sealing bar I0 is mounted foncooperation with a pressurebar generallydenoted` by Vreference numeral 22, comprisinga metal base 23. and anunderlying elastic layer 24 which mayadvantageously be formed of`silicone rubber. Pressure bar 22 is secured to areciprocable .support25 by means of bolts 26.

From the foregoing description, it ;Wi1l` be readily appreciated thatwhen thermoplasticlayers 2'I'and 28 to beheat sealed areintroduced 'l.between bars I0 and ZZ-.and thesaid bars are ycompressed by-means of asuitablereciprocating ymechanism (notshown), yielding and..elasticpressure willbe `applied to. bothfaces ofi-.the

v.thermoplastic layers.. ,This is .due to the. fact that .bothsealing-member II), aswell as pressure member 22 arecharacterizedbyvpressure-exerting surfaces ofelastic or compressible characterassured by the'provision offelasticlayers. I.2.and 24,. respectively.While the i elastic layer. I2 is .Y `not in direct contact with thematerials orlayers to be sealed, its elasticity iseirective to .asufficient extent through.A the..heater. element. I4 mounted thereon asa result of the yrelatively exible. character of the said element. As-it-has been .set forth4 inthe .foregoing-such, slightly 4elastic andconformable-character of the-operativefsurfaces ofboth pressuramembersor bars is quite benecial Whenlheatrsealing articlesthe thickness ofVwhich is not uniform throughout the sealing zone,. such being'ithecase,` forl exv ample, with gusseted-bags.

Considering now the modied embodiment of i. kthe invention shown in,Figs..3 `and 4, reference `numeral 30 generally denotes theheat-sealing .l member or .bar which. comprises a` rigid-metal member orbase 3l having a channel or U-.shaped cross section..` At each end ofsaid .channel- .shaped member, the side :Walls of the1member tom portionthereof, eis-indicated at 32.

,are cutaway, leaving onlythehorizontal or bot- In the channely member3| is i confinedy an elongated piece 33 of -elasticinsulating Vmaterial,such. as silicone rubber which issubstantiallyrectangular incrosssection and is of.such thickness as to 4 .extendsomewhat `abovevtheside wallsV of the channel member. Uponthe top surface of elastic"than the diameter of bolts 35.

layer or piece 33 is tensioned heater element 34 in the form of a thin,narrow and flexible metal band formed of metal of high specificresistance, same as heater element I4 in the previously describedembodiment of the invention. This is accomplished by means of bolts 35extending through aligned openings in heater element 34,

`elastic layer 33 and extensions 32 of channel member 3l. Bolts 35 aresecured by means of 'nuts 36, it being noted that the bolts areelecltrically insulated from extensions 32 of the channel member bymeans of insulating washers 31 and due to the fact that apertures 33 inthe said extensions are considerably larger in diameter Lead wires 39have their ends interposed between the heads of bolts 35 and theterminal portions of heater element 34 whereby the heater element may beconnected in circuit with a source of electrical 'impulses as this isset forth more fully in my screws 42 extending through apertures inmetal plates 4l and insulating layer 40 into threaded holes in the sideportions of the channel member.

The sealing bar 30 just described may be used in combination with apressure bar having an elastic pressure face, such as is shown at 22 inFig. 1. In the instant case, however, it is shown as being arranged forcooperation with a rigid bar 43 of metal of high heat conductivity, suchas copper, brass, or aluminum mounted for reciprocation on a support 44by means of bolts 45. This metal bar is provided with a longitudinallyextending channel 46 through which a flow of coolant fluid, such aswater, may be passed for the efficient withdrawal of heat therefrom.Nipples 41 are attached to the ends of channel 46 whereby a flexiblehose may be readily connected to each end of the channel for theintroduction and discharge of coolant uid.

In view of the similarity of construction the operation of this modifiedembodiment.y of the invention will be readily understood by thoseskilled in the art without any detailed description. It will besufficient to state that when layers 43 and 49 of thermoplastic materialare interposed between sealing bar 30 and pressure bar 43, thereciprocating means (not shown) are actuated and a pulse of current ispassed through heater element 34, a seal is formed in accordance withthe Well-known principles of thermal impulse sealing which are fullyexplained, for example, in my above-mentioned Patent No. 2,460,460. Theelastically yielding surface characteristics of sealing bar 36 willcompensate for any non-uniformity in the thickness of the layers to beheat sealed While the high heat conductivity of the face of pressuremember 43 will readily remove any residual heat from the sealed regionof the layers after each sealing operation, such Withdrawal of heatbeing further promoted, if desired, by the passage of coolant fluidthrough such member.

It will be noted that the present invention provides a number ofimportant advantages which may be summarized as follows:

1. The sealing pressure is maintained uniform even though the thicknessof the layers to be heat sealed or the number of such layers in thesealing zone may be subject to considerable variations. It has beenshown by actual experiments with heat sealing machines of the thermalimpulse type embodying the present invention that in articles in whichthe number of layers in the vsealing zone varies from 2 layers to 10layers,

satisfactory seals have been obtained in a single sealing operationwithout oversealing or scorching the region where only 2 layers werepresent or undersealing or producing an imperfect seal where as many as10 layers were present.

2. Minor misalignments in the parallelism of the sealing and pressurebars do not have any adverse effect on the operation of the machine.This is of considerable importance in heat sealing machines of thethermal impulse type having bars of accentuated length, such as Li2inches,

-or more, which are now in commercial production.

3. The combination of heat sealing bars of the thermal impulse type withrigid metal bars of high heat conductivity, which may be watercooled, ifdesired, any residual heat may be rapidly withdrawn from the sealingzone. This permits a substantial increase in the sealing speed which isan important factor when the thermal impulse principle is applied tohighspeed, automatic packaging machinery.

Although the present invention has been disclosed in connection with afew preferred embodiments thereof, variations and modifications may beresorted to by those skilled in the art without departing from theprinciples of the invention. I consider all of these variations andmodifications to be within the true spirit and scope of the presentinvention, as disclosed in the foregoing description and defined by theappended claims.

I claim:

1. A sealing bar for heat sealing machines comprising, in combination, asubstantially rigid backing member, a layer of elastic insulatingmaterial thereon, and an elongated directly heated flexible metal membermounted on said layer and constituting a heater element adapted toyieldingly conform to the surface of the materials to be heat sealed.

2. .A sealing bar for heat sealing machines of the thermal impulse typecomprising, in combination, a substantially rigid backing member, a

layer of heat-resistant elastic insulating material thereon, a flexiblemetal strip tensioned on said layer, said strip being adapted to beheated to heat sealing temperatures by the passage of electric currenttherethrough and to conform to the surface contour of the layers to beheat sealed as a result of its flexibility and of the elasticity of theunderlying layer, and a layer of heat-resistant flexible insulatingmaterial overlying said metal strip and being sufficiently thin toassure the rapid transmission of sealing heat therethrough.

3. A sealing bar for heat sealing machines of the thermal impulse typecomprising, in combination, a substantially rigid backing member, alayer of heat-resistant elastic insulating material thereon, a flexiblemetal strip tensioned on said layer, said strip being less in width thansaid layer and being adapted to be heated to heat seal- Y ingtemperatures by the passage of electric current therethrough and toconform to the surface contourof the layersfto be heat-,sealedpandsialayer of heat-resistant:xexible insulatingfmaterial. overlying* saidImetalv strip and said' elastic layer and said` backing member --andbeing sufficiently thinto assure-the rapid transmissionof i saidmetalstrip and said elasticrbody 'and being suflcientlyA thin to assur-ethe rapidtransmission of sealing heat i therethroughy said `layer.constitutingthe operative `and sealing face of -the bar.

5. In a machine for heat sealing thermoplastic layers, the combinationwhich comprises-1a sealing `bar including a rigid back-ing member, ualayerof elastic materialithereon, anda flexible metalstrip mounted onsaid layer and'consttuting therewithy an electricheater'elementconformable to the surface-contour of thelayersto be heat sea1ed;and alrigid pressure bar of high-heat conductivity metal mounted forcooperation with saidssealingbarand adapted to Withdraw `heat from thethermoplasticlayersinterposed between saidl bars after the sealingoperation.A

6. The machine claimed in claim 45 wherein the Width of the flexiblemetal strip is less than that of the underlying elastic layer and thatof the rigid pressure Abar and Wherein a channel is provided in therigid pressure bar forthe -passage of coolant iluid therethrough;

7 In a machine for heat sealing thermoplastic layers, the combinationwhich comprises `a sealing bar including a rigid backing member, a layerof heat-resistant elastic insulating material thereon, a flexible metalstrip tensioned on said layer, and a thin layer of heat-resistantflexible insulating material overlying saidelastic layer and said metalstrip and constituting `a yieldingly conformable sealing face for thebar; and a rigid pressure bar of high heat conductivity metal mountedfor cooperation with said sealing bar and adapted 'to withdraw heat fromthe thermoplastic layers interposed between said bars .after the sealingoperation.

References Cited in the file of this patent f UNITED STATES PATENTS l`Number Name Date 2,289,618 Young July 14, 1942 2,574,094 Fener et alNov. 6, 1951 2,574,095 Langer Nov. 6, 1951 2,614,953 Anglada Oct. 21,1952

